Inhaled aerosol particle dosimetry in mice: A review

Macrophage-mediated tissue response evoked by subchronic inhalation of lead oxide nanoparticles is associated with the alteration of phospholipases C and cholesterol transporters

Background

Inhalation of lead oxide nanoparticles (PbO NPs), which are emitted to the environment by high-temperature technological processes, heavily impairs target organs. These nanoparticles pass through the lung barrier and are distributed via the blood into secondary target organs, where they cause numerous pathological alterations. Here, we studied in detail, macrophages as specialized cells involved in the innate and adaptive immune response in selected target organs to unravel their potential involvement in reaction to subchronic PbO NP inhalation. In this context, we also tackled possible alterations in lipid uptake in the lungs and liver, which is usually associated with foam macrophage formation.

Results

The histopathological analysis of PbO NP exposed lung revealed serious chronic inflammation of lung tissues. The number of total and foam macrophages was significantly increased in lung, and they contained numerous cholesterol crystals. PbO NP inhalation induced changes in expression of phospholipases C (PLC) as enzymes linked to macrophage-mediated inflammation in lungs. In the liver, the subchronic inhalation of PbO NPs caused predominantly hyperemia, microsteatosis or remodeling of the liver parenchyma, and the number of liver macrophages also significantly was increased. The gene and protein expression of a cholesterol transporter CD36, which is associated with lipid metabolism, was altered in the liver. The amount of selected cholesteryl esters (CE 16:0, CE 18:1, CE 20:4, CE 22:6) in liver tissue was decreased after subchronic PbO NP inhalation, while total and free cholesterol in liver tissue was slightly increased. Gene and protein expression of phospholipase PLCβ1 and receptor CD36 in human hepatocytes were affected also in in vitro experiments after acute PbO NP exposure. No microscopic or serious functional kidney alterations were detected after subchronic PbO NP exposure and CD68 positive cells were present in the physiological mode in its interstitial tissues.

Conclusion

Our study revealed the association of increased cholesterol and lipid storage in targeted tissues with the alteration of scavenger receptors and phospholipases C after subchronic inhalation of PbO NPs and yet uncovered processes, which can contribute to steatosis in liver after metal nanoparticles exposure.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12989-022-00494-7.

Acute neuroradiological, behavioral, and physiological effects of nose-only exposure to vaporized cannabis in C57BL/6 mice

Objective: The rapid increase of cannabis consumption reinforces the need to elucidate the health hazards of this practice. The presence of fine particulate matter in cannabis smoke and vapor poses a major concern, as it may contribute to cardiopulmonary disease. To facilitate the assessment of risks associated with cannabis inhalation, we developed and characterized a method for exposing mice to cannabis in a way that mimics the delivery of the drug to the airways of smokers. Materials and Methods: Cannabis (10.3% THC, 0.05% CBD) was vaporized to generate aerosols with a reproducible particle profile. Aerosols were acutely delivered to male, adult C57BL/6 mice via a nose-only exposure system. Serum THC levels were measured for increasing cannabis doses. Blood pressure and heart rate were recorded at baseline and following exposure. Behavioral response to cannabis inhalation in the open field was documented. Awake neurological activity upon cannabis exposure was monitored using BOLD fMRI.Results and Discussion: Cannabis aerosols contained particles with count median diameter of 243 ± 39 nm and geometric standard deviation of 1.56 ± 0.06. Blood serum THC levels increased linearly with aerosolized mass and peaked at 136 ± 5 ng/mL. Cannabis inhalation decreased heart rate and blood pressure but promoted anxiety-like behavior. Observed differences in BOLD activation volumes linked cannabis to increased awareness to sensory stimuli and reduced behavioral arousal.Conclusions: Quantified physiological, behavioral, and neurological responses served as validation for our mouse model of cannabis inhalation. Animal models of aerosol exposure will be instrumental for uncovering the health outcomes of chronic cannabis use.

The fractal geometry of bronchial trees differs by strain in mice

Fractal biological structures are pervasive throughout the plant and animal kingdoms, with the mammalian lung being a quintessential example. The lung airway and vascular trees are generated during embryogenesis from a small set of building codes similar to Turing mechanisms that create robust trees ideally suited to their functions. Whereas the blood flow pattern generated by these fractal trees has been shown to be genetically determined, the geometry of the trees has not. We explored a newly established repository providing high-resolution bronchial trees from the four most commonly studied laboratory mice (B6C3F1, BALB/c, C57BL/6 and CD-1). The data fit a fractal model well for all animals with the fractal dimensions ranging from 1.54 to 1.67, indicating that the conducting airway of mice can be considered a self-similar and space-filling structure. We determined that the fractal dimensions of these airway trees differed by strain but not sex, reinforcing the concept that airway branching patterns are encoded within the DNA. The observations also highlight that future study design and interpretations may need to consider differences in airway geometry between mouse strains.NEW & NOTEWORTHY Similar to larger mammals such as humans, the geometries of the bronchial tree in mice are fractal structures that have repeating patterns from the trachea to the terminal branches. The airway geometries of the four most commonly studied mice are different and need to be considered when comparing results that employ different mouse strains. This variability in mouse airway geometries should be incorporated into computer models exploring toxicology and aerosol deposition in mouse models.

Modeling particle deposition in the Balb/c mouse respiratory tract

The mouse lung has become increasingly important as a surrogate of the human lung for inhalation risk assessment. The main structural difference between the two lungs is that the airway branching of the human lung is relatively symmetric, while that of the mouse lung is distinctly asymmetric or monopodial. The objectives of this study were to develop a stochastic, asymmetric particle deposition model for the Balb/c mouse and to compare predicted deposition patterns with those in the human lung. The asymmetric bronchial airway geometry of the Balb/c mouse was based on a statistical analysis of several lung casts, while, in the absence of pertinent data, the asymmetric acinar airway geometry was represented by an allometrically scaled-down version of the rat acinar region, assuming structural similarity. Deposition of inhaled particles in nasal, bronchial and acinar airways for mouse-specific breathing conditions was computed with the Monte Carlo deposition model IDEAL-mouse. While total deposition for submicron particles decreases with increasing diameter in a fashion similar to that in the human lung, the effect of inhalability and nasal pre-filtration significantly reduces total deposition in the mouse lung for particles with diameters greater than about 3 μm. The most notable difference between submicron particle deposition in the mouse and human airways is the shift of the deposition distribution from distal airway generations in the human lung to upper airway generations in the mouse lung. However, if plotted as a function of airway diameter, both deposition distributions are quite similar, indicating that airway diameter may be a more appropriate morphometric parameter for extrapolation purposes than airway generation.

A comparative assessment of the acute inhalation toxicity of vanadium compounds

Vanadium compounds have become important in industrial processes, resulting in workplace exposure potential and are present in ambient air as a result of fossil fuel combustion. A series of acute nose-only inhalation toxicity studies was conducted in both rats and mice in order to obtain comparative data on the acute toxicity potential of compounds used commercially. V₂O₃, V₂O₄, and V₂O₅, which have different oxidation states (+3, +4, +5, respectively), were delivered as micronized powders; the highly water-soluble and hygroscopic VOSO₄ (+4) could not be micronized and was instead delivered as a liquid aerosol from an aqueous solution. V₂O₅ was the most acutely toxic micronized powder in both species. Despite its lower overall percentage vanadium content, a liquid aerosol of VOSO₄ was more toxic than the V₂O₅ particles in mice, but not in rats. These data suggest that an interaction of characteristics, i.e., bioavailability, solubility and oxidation state, as well as species sensitivity, likely affect the toxicity potential of vanadium compounds. Based on clinical observations and gross necropsy findings, the lung appeared to be the target organ for all compounds. The level of hazard posed will depend on the specific chemical form of the vanadium. Future work to define the inhalation toxicity potential of vanadium compounds of various oxidation states after repeated exposures will be important in understanding how the physico-chemical and biological characteristics of specific vanadium compounds interact to affect toxicity potential and the potential risks posed to human health.

Computational modeling of nanoscale and microscale particle deposition, retention and dosimetry in the mouse respiratory tract

Comparing effects of inhaled particles across rodent test systems and between rodent test systems and humans is a key obstacle to the interpretation of common toxicological test systems for human risk assessment. These comparisons, correlation with effects and prediction of effects, are best conducted using measures of tissue dose in the respiratory tract. Differences in lung geometry, physiology and the characteristics of ventilation can give rise to differences in the regional deposition of particles in the lung in these species. Differences in regional lung tissue doses cannot currently be measured experimentally. Regional lung tissue dosimetry can however be predicted using models developed for rats, monkeys, and humans. A computational model of particle respiratory tract deposition and clearance was developed for BALB/c and B6C3F1 mice, creating a cross-species suite of available models for particle dosimetry in the lung. Airflow and particle transport equations were solved throughout the respiratory tract of these mice strains to obtain temporal and spatial concentration of inhaled particles from which deposition fractions were determined. Particle inhalability (Inhalable fraction, IF) and upper respiratory tract (URT) deposition were directly related to particle diffusive and inertial properties. Measurements of the retained mass at several post-exposure times following exposure to iron oxide nanoparticles, micro- and nanoscale C60 fullerene, and nanoscale silver particles were used to calibrate and verify model predictions of total lung dose. Interstrain (mice) and interspecies (mouse, rat and human) differences in particle inhalability, fractional deposition and tissue dosimetry are described for ultrafine, fine and coarse particles.

Ozone co-exposure modifies cardiac responses to fine and ultrafine ambient particulate matter in mice: concordance of electrocardiogram and mechanical responses

Background

Studies have shown a relationship between air pollution and increased risk of cardiovascular morbidity and mortality. Due to the complexity of ambient air pollution composition, recent studies have examined the effects of co-exposure, particularly particulate matter (PM) and gas, to determine whether pollutant interactions alter (e.g. synergistically, antagonistically) the health response. This study examines the independent effects of fine (FCAPs) and ultrafine (UFCAPs) concentrated ambient particles on cardiac function, and determine the impact of ozone (O₃) co-exposure on the response. We hypothesized that UFCAPs would cause greater decrement in mechanical function and electrical dysfunction than FCAPs, and that O₃ co-exposure would enhance the effects of both particle-types.

Methods

Conscious/unrestrained radiotelemetered mice were exposed once whole-body to either 190 μg/m³ FCAPs or 140 μg/m³ UFCAPs with/without 0.3 ppm O₃; separate groups were exposed to either filtered air (FA) or O₃ alone. Heart rate (HR) and electrocardiogram (ECG) were recorded continuously before, during and after exposure, and cardiac mechanical function was assessed using a Langendorff perfusion preparation 24 hrs post-exposure.

Results

FCAPs alone caused a significant decrease in baseline left ventricular developed pressure (LVDP) and contractility, whereas UFCAPs did not; neither FCAPs nor UFCAPs alone caused any ECG changes. O₃ co-exposure with FCAPs caused a significant decrease in heart rate variability when compared to FA but also blocked the decrement in cardiac function. On the other hand, O₃ co-exposure with UFCAPs significantly increased QRS-interval, QTc and non-conducted P-wave arrhythmias, and decreased LVDP, rate of contractility and relaxation when compared to controls.

Conclusions

These data suggest that particle size and gaseous interactions may play a role in cardiac function decrements one day after exposure. Although FCAPs + O₃ only altered autonomic balance, UFCAPs + O₃ appeared to be more serious by increasing cardiac arrhythmias and causing mechanical decrements. As such, O₃ appears to interact differently with FCAPs and UFCAPs, resulting in varied cardiac changes, which suggests that the cardiovascular effects of particle-gas co-exposures are not simply additive or even generalizable. Additionally, the mode of toxicity underlying this effect may be subtle given none of the exposures described here impaired post-ischemia recovery.

Electronic supplementary material

The online version of this article (doi:10.1186/s12989-014-0054-4) contains supplementary material, which is available to authorized users.